1. Field of the Invention
The present invention relates to foamed completion fluids and methods of completing subterranean zones utilizing the foamed completion fluids.
2. Description of the Prior Art
The completion process prepares a well for production and the fluids used at that stage of well construction are called “completion fluids.” Initially, drilling fluids were used as completion fluids. Once perforating wells became a normal practice, it was found that using clean, solids-free brines for perforating increases well productivity. Well completion practices consisted of cementing casing, displacing the drilling fluid with a completion fluid and then perforating the well. Once the directional drilling evolved to horizontal and multilateral well designs and sand control in unconsolidated formations, the completion technology became more complex. As a result, specialized completion fluid technology has been developed and completion fluids are frequently used for perforating, forming gravel packs and other well operations such as the placement of tubing, packers, pumps and the like.
The aqueous completion fluids utilized are clean, relatively solids free, include one or more dissolved salts that provide weight to the completion fluids and do not react with the subterranean formation rock or hydrocarbons contained therein.
Completion fluids must also be compatible with formation clays to prevent clay swelling or deflocculating which causes the pore spaces in the subterranean formation to become blocked. Further, the completion fluids must be compatible with formation crude oil and natural gas so that oil-water emulsions are not formed which may produce formation damage.
The weight of an aqueous completion fluid can be adjusted by mixing one or more salts with the fluids, e.g., calcium chloride and calcium bromide. In order to prevent loss of the completion fluid, fluid loss control additives can be included in the completion fluids. Also, the rheology of a completion fluid can be controlled by the addition of friction reducers and/or lowering the viscosity of the completion fluid.
Thus, a completion fluid must be heavy enough to control formation pressure, be solids free, have minimum or no fluid loss to the producing formation and prevent damage to the formation.
While foamed completion fluids have been utilized heretofore, it has been difficult to form stable foamed completion fluids, particularly those completion fluids containing zinc bromide and other salts.
Thus, there is a need for foamed completion fluids formed of water, one or more salts, a gas and a foaming agent that are extremely stable.